1. Field of the Invention
The present invention generally relates to a curing component for epoxy resins, epoxy resins containing the curing component and to the use thereof.
2. Description of Related Art
It is known that alcohols, in particular phenol or alkylated phenols, accelerate the curing reaction between oxiranes and amino groups (cf. U.S. Pat. No. 3,366,600 and DE-A 17 70 832). It has proven advantageous in these processes to combine the phenol component together with the amine component in one molecule. In DE-A 15 43 754, a hydroxyaryl-substituted aliphatic carboxylic acid is linked with a polyamine via an amide bond for this purpose. In this process, however, one amino group of the polyamine, which is required for the amide bond, is lost to the curing operation.
DE-A 32 33 565 and EP-B 0 114 875 therefore propose, as the curing component, the reaction product of a Mannich reaction of aldehydes and polyamines with phenol or alkylphenols, for example cresols, p-tert-butylphenol or nonylphenol, and EP-A 0 066 447 also with arylphenols, for example benzylphenol.
These combinations have proven suitable, but the combinations also display disadvantages, such as, a lack of acceleration at low temperatures (.ltoreq.10.degree. C.) and under high atmospheric humidity. These combinations also exhibit a lack of resistance to dilute organic acids, for example acetic acid. Since phenol or alkylated phenols are contained in all of these combinations, they are also of only limited applicability from the toxicological point of view, because of the risk to the user during application. Furthermore, for example, the phenols are easily extracted from the coating on contact with foods, due to the aqueous-dilute organic acids contained therein, such as acetic acid, tartaric acid or citric acid, and spoil the food.
DE-B 10 43 629 also mentions polyhydric phenols, in addition to the customary phenolic components, as possible reactants for curing components which can be prepared by the Mannich reaction. Compounds such as resorcinol and hydroquinone, however, give highly crosslinked Mannich bases of undesirably high viscosity because of their high reactivity. Moreover, the increased polarity of polyhydric phenols, compared with monohydric phenolic components, causes relatively severe blushing of coatings produced from curable mixtures comprising polyhydric phenols.